In the continuous casting of steel the metal is tranfered into successive vessels such as ladles and distributors. One or more tapholes are provided in the bottom of each container for casting the metal.
The flow can be regulated by different means such as plate closures, stopper rods or simply a calibrated nozzle.
Some applications call for protection of the molten metal from the surrounding air. A refractory protection tube is then fastened under the vessel to surround the stream of molten metal as it emerges from the pouring hole.
Whatever the type of pouring refractory used, these refractories wear out and have to be changed so that the casting can be continued with the same vessel. Various solutions are already known for exchanging refractories without interrupting the pouring. For example, Belgian Patent N.degree. 214,385 describes a tube changing device.
In a device of this type the a fixed plate. A lower plate combined with a protection tube is laid against the fixed plate to assure a tight joint.
When this plate and the protection tube associated with it have to be replaced, the plate of a new plate/tube assembly is placed alongside the plate to be changed and pushed by adequate means. The new plate expels the worn plate and takes its place.
To assure a perfect alignment of the upper face of the lower plate with the lower face of the upper plate, the fixed upper plate is generally longer than the lower plate at least on the side of introduction of the replacement plate so that the new plate can be introduced against the end of the upper plate when the plate to be replaced is still in the pouring position.
These places are frequently surrounded with a metal envelope. The use of a metal envelope makes it possible to obtain a plate ready for use, the outside dimensions of which are well-defined and which has resistant integrated sliding and support surfaces.
The metal envelope also permits maintaining the cohesion of the refractory material when cracks appear under the effect of thermal and mechanically elevated stresses induced by the casting conditions.
Exposition of the technical problem
Because the upper plate is longer, it is also more costly to produce.
On the other hand, the fact that the dimensions of the plates are different necessitates the management of different components, particularly when the refractory plates are surrounded by a metal envelope, the production of which requires a costly investment in tooling equipment. The purpose of the present invention is a plate changing device that resolves these disadvantages.
According to the invention, the upper plate and the lower plate have identical polygonal peripheries and are angularly offset so that they do not overlap completely.
Thus, the surface of the fixed plate directed toward the replacement plate that is not covered by the plate during pouring can serve as a guide surface for the replacement plate. Thus, although the surfaces of the plates are equal, we have a guide surface that permits a perfect alignment of the upper face of the lower plate with the lower surface of the upper plate.
Furthermore, the same metal envelope can be used for the two types of plates, also in the case where their internal constitution is different. The cost of the tooling equipment necessary for producing the metal envelopes is cut in half.
Preferably, the polygonal periphery of the plates is a square and a pouring orifice is placed in the center of the square.
Also preferably, the fixed plate and the replaceable plate are offset angularly by 45.degree.. Preferably, the two surfaces lateral to the direction of introduction of the plates of the fixed plate which are never covered by the lower plate, either when the plates are in the casting position or during the changing of plates, are used to fix it on the device chassis, for example, by means of screws with a conical end, each acting on one edge of the fixed plate situated in the lateral zone not covered by the lower plate, these edges being situated at the front of this fixed plate with respect to the direction of introduction of the replacement plates in order to move the fixed plate simultaneously towards the back and against the drawer chassis.
This assures that during successive plate changes the upper plate will remain fixed and the joint between the upper plate and the well block or inner nozzle will not be damaged.